Let There Be (More) Light

In photography, light is the most important thing. In daytime shots, natural light is your friend. When dealing with astrophotography however, we are imaging small points of light — the stars. It is important therefore to take longer exposure shots to let in more light to the camera. Slow shutter speeds make it challenging to avoid blur, camera shake and vibrations. A sturdy tripod is essential.

Sharp images are key in photography. Autofocus won’t work most of the time for astrophotos, so it is important to focus manually. For adigital SLR camera it is very difficult to use a viewfinder alone by eye, so a “live-view” gives you the best view. Zooming in can help you see if the stars appear sharp.

This panorama photo, taken by ESO Photo Ambassador Yuri Beletsky, shows the view of the starry sky from the site of ESO’s Very Large Telescope (VLT) at Cerro Paranal during the total lunar eclipse of 21 December 2010. Credit: ESO/Y. Beletsky

You need to do everything possible to let as much light as possible into the camera, and shoot under the darkest conditions possible. It is best to use a lens with the largest aperture possible, as indicated by the F-number (F-ratio or focal ratio). Increasing the film speed(ISO setting) will also let in more light, although this will increase the noise in the shot. It is usually best to take several images and then add them together (stack them) afterwards to form a composite with greater detail and depth.

Gaze up at the night sky from ESO's Paranal Observatory in Chile, and you will be greeted with a stunning view like this one. Flecks of blue, orange, red; each a different star, galaxy, nebula, or more, together forming a sparkling sky overhead. Astronomers peer at this beautiful backdrop, trying to unravel the mysteries of the Universe. Credit: ESO/Y. Beletsky

Be aware of light pollution, an increasing problem for astronomers, especially in densely populated regions in Europe and North America. This is light you don’t want! We are very fortunate to be able to image from some of the best and darkest skies in the world from ESO’s sites in Chile. Here’s one of my favourite shots from Paranal. One can see the enclosures housing the 1.8-metre Auxiliary Telescopes (ATs) that are used for interferometry. Above these three ATs, the Large and Small Magellanic Clouds are the satellite galaxies of the Milky Way. They are only seen from the southern hemisphere.

The conditions are so great, the skies so dark and the atmosphere so steady that the stars seem like jewels in the night sky that you can just touch. Remarkably, the green and red cast along the horizon is not light pollution. This is actually airglow — a very weak emission of light in the Earth’s atmosphere.